1. Field of the Invention
The present invention relates to piezoelectric drive elements for writing jets, particularly of the type utilized in mosaic ink printing devices in which a writing fluid contained in a compression chamber cylindrically enclosed by the drive element is ejected in droplets by controlled contraction of the compression chamber.
2. Description of the Prior Art
Utilization of piezoelectric material for the drive element of writing jets in ink printing devices is well known in the art. A piezoelectric drive element for writing jets is known, for example, from German AS No. 25 37 767 and the employment of this effect in a mosaic ink printing device is disclosed, for example, in German AS No. 25 48 691, corresponding to U.S. Pat. No. 1,161,670.
In known arrangements of the above type, tubular drive elements of polarized ceramic cylindrically enclose a writing fluid channel. The interior diameter of each of the drive elements is reduced upon the application of an electrical voltage having a polarity in the direction of the polarization voltage of the ceramic, and is expanded upon application of an electrical voltage having a plurality opposite to the polarization voltage. By the use of a suitable drive circuit, the piezoelectric drive element is first expanded and then driven into a constricted state by reversal of polarity of the voltage, resulting in ejection of a writing fluid droplet. Such devices require voltage of more than 80 volts supplied in pulse-form for the operation thereof. Such a circuit requires a considerable outlay in expense for an entire spray head inasmuch as a pulse generating circuit must be present for each of the piezoelectrically driven writing jets.
It is a problem in the art to provide a piezoelectric drive element for a writing jet having decreased voltage requirements and thus requiring decreased circuit outlay for driving of the piezoelectric element.